A design method of compound free space optical/millimeter wave (FSO/MMW) antenna for point-to-point communication is proposed. A hybrid transmission line theory-ray tracing method (TLT-RTM) is proposed for rapid and efficient simulation of the FSO/MMW antenna, which contains an absorption dielectric material with electrically large size. Meanwhile, a compound antenna is optimized using TLT-RTM. The working wavelength of the compound antenna in optical spectrum is 1550 nm and the microwave frequency is 28 GHz. The aperture of the compound antenna is 200 mm and the effective focal length is 816.86 mm. The spatial frequency is 30 lp/mm when the contrast transfer function is reduced to 0.7 for optical wave. The gain of the compound antenna is 32.97 dBi and the half power bandwidth is 3.29° for millimeter wave. The compound antenna can be applied to transmitting optical and millimeter wave signals at the common aperture in point-to-point terrestrial links of 5G communication networks.